Fiends
Fiends, sometimes called Devils, are the acolytes of Aldem, King of all Hells. There are an evil cast of heinous creatures. They are either the descendants of, or the very beings who were created long ago to destroy Goh’zul.
Long before The Sea of Monsters even existed. Goh’zul was a being who had the power to create worlds, grow them, and devour them to satiate his endless hunger. Many of the worlds he made were aware of his existence, and tried to stop their destruction. A strange, repeating phenomenon occurred in many of these realms. Legions of Fiends were made by the gods of these long dead worlds in a futile attempt to strike back at Goh’zul. They would be given a realm of their own, called a Hell. It is not know why this phenomenon happened so regularly. Perhaps it was part of Goh’zul’s design, or perhaps it was just convergent evolution of these worlds.
As a method of payment, the gods would often send the souls of sinners to the fiends as payment. It is not known why this transaction was made, but many assume it was for sustenance or to entertain them. Regardless, the exchange largely kept them at bay.
Despite the efforts of these worlds, it was never enough to defeat him. When he would consume them, he would leave the hells undigested (for lack of a better term). They sat trapped in his body for eons. Eventually, they began colliding and merging. When they all formed into one singular, colossal realm, a massive war amongst them eventually left Aldem, King of all Hells as their ruler.
Not all Fiends are evil, supposedly some of them in Apolyatum are quite reasonable and person-like. However the vast majority are nefarious and horrifying. Their once mission to destroy Goh’zul, and their hatred towards him for trapping them in his body like a prison has only fortified their original mission to destroy him. However, since he is dead that hate is instead aimed at the world of Zol.
Demons are distinctly different from Fiends. Fiends are forced to serve Aldem, King of all Hells. If they resist him, they are destroyed. Demons are largely unbound, and can do what they wish. This makes many Demons prideful over Fiends, fueling a rivalry between the two casts of horrible creatures.